Blowing agent-containing polymeric MDI compositions

ABSTRACT

Mixtures of medium viscosity polymeric MDI and HCFC-22 have unexpectedly low vapor pressure, rendering such mixtures suitable for the preparation of polyurethane and polyisocyanate foams.

This is a division of application Ser. No. 07/858,787 filed Mar. 27,1992.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention pertains to isocyanate compositions containingblowing agents. More particularly, the subject invention pertains tocompositions comprising medium viscosity polymericmethylenediphenylenediisocyanates (polymeric MDI) andmonochlorodifluoromethane.

2. Description of the Related Art

Polymeric MDI is a valuable commodity whose largest commercial use is inthe preparation of rigid polyurethane foams, particularly insulatingfoams for refrigerators, freezers, and roofing and siding laminateboards. At present, the majority of such rigid foams are blown withmonochlorotrifluoromethane, refrigerant 11, a CFC which has come underincreasing disfavor due to its ozone depletion potential.Monochlorodifluorometnane, an HCFC, has been proposed as a substitutefor R-11, due to the fact that its ozone depletion potential is onlyc.a. 5% of R-11. However, R-22 is a gas at room temperature while R-11is a liquid, and thus its use is problematic. Polyol mixtures containingR-22 develop considerable vapor pressure, for example, which can createproblems when drums or tank cars are exposed to high temperatures. Theatmospheric pressure solubility of HCFC-22 in polyester polyols andpolyether polyols, for example, is only about 3 and 5 weight percentrespectively.

One possible solution to this problem is to incorporate R-22 blowingagent in both the polyol component and isocyanate component of thepolyurethane system. Unfortunately, the vapor pressure in the isocyanatecomponent can still present a problem.

SUMMARY OF THE INVENTION

It has now been unexpectedly discovered that medium viscosity polymericMDI will hold more R-22 in solution at a given pressure than polymericMDI having lower or higher viscosities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Polymeric MDI is prepared by the reaction of aniline with formaldehyde,followed by phosgenation and thermal cleavage into a crude mixture ofisocyanates. By suitable selection of the aniline/formaldehyde ratio andthe reaction conditions, the amount of two-ring versus higherring-content analogues can be adjusted. The isocyanates preparedaccording to this process correspond to the formula: ##STR1## Thecontent of higher ring-content analogues (n>O) determines to a greatextent the viscosity of the mixture. Most frequently, the crude reactionmixture is subjected to partial distillation to remove the higher valuetwo ring components. As a result of the distillation, the viscosity ofthe pot residue increases. The end result is the ability of themanufacturer to offer polymeric MDI with a range of viscosities andfunctionalities, which can be adjusted, if necessary by the addition oflower viscosity polymeric MDI, two-ring MDI, or higher viscositypolymeric MDI. The preparation of such polymeric MDI mixtures is wellknown to those skilled in the art.

As the viscosity of the polymeric MDI is determined essentially by theamount of higher ring "polymeric" species, one would expect that thesolubility of gaseous blowing agent in polymeric MDI would be a functionof viscosity, either steadily decreasing with higher 2-ring content(lower viscosity) or steadily increasing. However, it has unexpectedlybeen found that such is not the case, and that the solubility of HCFC-22is much greater, at a given pressure, in medium viscosity polymeric MDI,i.e. MDI having a viscosity of from about 400 cps to about 1200 cps,preferably 600 cps to 1000 cps, than polymeric MDI having lower orhigher viscosity. Thus medium viscosity polymeric MDI mixturescontaining HCFC-22 are suitable for preparing polyurethane foams inprocesses where the use of otherwise similar mixtures containing loweror higher viscosity polymeric MDI would not be suitable due to equipmentlimitations or safety considerations, particularly in production wherethe isocyanate component is stored in drums or tanks incapable ofwithstanding more than modest pressure.

The medium viscosity polymeric MDI of the subject invention may furthercontain a minor portion, not to exceed about 30 percent by weight basedon the weight of total isocyanate, preferably less than 20 percent byweight and most preferably less than 10 percent by weight of a modifiedtwo-ring MDI or modified polymeric MDI wherein the modified MDI orpolymeric MDI contains urethane or carbodiimide linkages. Such modifiedisocyanates are available commercially as Lupranate™ MP-102, a urethanemodified two-ring MDI, and Lupranate™ MM-103, a carbodiimide modifiedtwo-ring MDI. Other urethane modified MDI's based on polymeric MDI arealso available.

The polyurethane foams prepared from the medium viscosity polymericMDI/HCFC-22 mixtures are generally of the rigid type, with predominatelyclosed cells, although open cell foams may be suitable for manyapplications, for example picnic coolers. These foams are prepared, asis well known to those skilled in the polyurethane art, by reacting apolyol component generally comprising polyether or polyester polyolswith the isocyanate component, at isocyanate indexes of from 70 to 900,preferably 90 to 400. At indexes close to 100, the foam chemistry issuch that the predominate linkages are urethane, while at significantlyhigher indexes, i.e. 200-900, the linkages are predominatelyisocyanurate. Polyisocyanurate foams have been particularly difficult toprepare with gaseous blowing agents, since the small amount of polyolcomponent renders it highly difficult to include the necessary amount ofblowing agent. With the medium viscosity polymeric MDI/HCFC-22 mixturesof the subject invention, such foams are possible using nearlyconventional technology.

Further, the foam quality using medium viscosity polymeric MDI/HCFC-22mixtures may be improved over that expected with higher or lowerviscosity polymeric MDI's, particularly the latter, since upon exit fromthe mix head, the reaction mass, finding itself now at atmosphericpressure, tends to froth, often leading to large "bubbles" rather thanfine cells. As the vapor pressure of HCFC-22 is lower in mediumviscosity polymeric MDI at a given HCFC-22 weight percent concentration,these frothing problems can be minimized.

The invention will now be illustrated by the following examples. In theexamples, HCFC-22 was metered into a stainless steel bomb having aninternal volume of approximately 1 liter containing several stainlesssteel balls to allow for thorough mixing, and the amount of HCFC-22added under pressure determined by weighing the bomb. The bomb, inaddition to being equipped with an inlet value for HCFC-22 was alsoequipped with a connection for a pressure transducer. The bomb wasevacuated prior to addition of HCFC-22, and thus the pressures measuredare in pounds per square inch absolute (psia). In the first two trials,with medium and high viscosity polymeric MDI, the bomb was maintained at75° F. after each HCFC-22 addition, and shaken several times over aperiod of approximately one half hour. The pressure was then measured.In trial 3, with low viscosity polymeric MDI, HCFC-22 was added at 2.3weight percent, and the pressure after equilibration at severaltemperatures measured. The results are presented below.

                  TABLE 1                                                         ______________________________________                                                   Weight percent HCFC-22 at Pressure                                            (psia).sup.1                                                       Isocyanate  15       30    45    60  75     90                                ______________________________________                                        Medium Viscosity.sup.2                                                                     5.0     6.6   8.0   9.5 11.1   12.7                              High Viscosity.sup.3                                                                      <2.5     4.0   5.7   7.2 --     --                                ______________________________________                                         .sup.1 Values interpolated from a plot of pressure versus weight percent.     .sup.2 Lupranate ™ M70L, a polymeric MDI having a nominal viscosity of     700 cps.                                                                      .sup.3 Lupranate ™ M200, a polymeric MDI having a nominal viscosity of     2000.                                                                    

In trial 3, at 2.3 weight percent HCFC-22 concentration in a lowviscosity polymeric MDI having a nominal viscosity of 200 cps(Lupranate™ M20S), the pressures (psia) at various temperatures aregiven below.

                  TABLE 2                                                         ______________________________________                                        Temperature (°C.)                                                                      Pressure (psia)                                               ______________________________________                                        21              27.4                                                          42              48.5                                                          60              67.7                                                          ______________________________________                                    

Thus, at only 2.3 weight percent HCFC-22, the pressure at 21° C. (70°F.) is 27.4 psia, while with medium viscosity polymeric MDI at 75° F. 5°F. higher the weight percent of HCFC-22 at 27.4 psia is approximately6.5 weight percent, approximately 300 percent higher.

What is claimed is:
 1. A composition comprising medium viscositypolymeric MDI methylenediphenylenediisocyanate having a viscosity offrom 400 to 1200 centipoise when measured at 25° C., andmonochlorodifluoromethane.
 2. The composition of claim 1 wherein saidmedium viscosity polymeric methylenediphenylenediisocyante has aviscosity of from 600 to 1000 centipoise when measured at 25° C.
 3. Thecomposition of claim 1 wherein said monochlorodifluoromethane is presentin an amount of from 4 weight percent to about 12 weight percent basedon the total composition.
 4. The composition of claim 2 wherein saidmonochlorodifluoromethane is present in an amount of from 4 weightpercent to about 12 weight percent based on the total composition. 5.The composition of claim 1, further comprising a minor quantity, not toexceed 30 percent by weight of total isocyanate of a modified tow-ringmethylenediphenylenediisocyanode or modified polymericmethlenediphenylenediisocyanode wherein said modifiedmethylenediphenylenediisocyanate or polymericmethylenediphenylenediisocyanate contains urethane or carbodiimidelinkages.